1. Field of the Invention
This invention relates to sealed shaft journal bearings and more particularly to an improved bearing assembly employing a seal wear ring including a substantially cylindrical metal sleeve having an inside diameter greater than that of the shaft with which the bearing is used and an annular spacer ring formed from a low friction synthetic resin material mounted within the metal sleeve and dimensioned to provide an interference fit with the shaft surface.
2. Description of the Prior Art
Roller bearing assemblies incorporating two rows of tapered roller bearings preassembled into a self-contained, pre-lubricated package for assembly onto journals at the ends of axles or shafts are well known. Such bearing assemblies are widely used as rail car bearings assembled onto journals at the ends of the car axles and the present invention will be described with reference to such rail car bearings, it being understood that the invention is not so limited but rather that the bearings may be employed on shaft journals for various uses. Bearings of this type typically employ two rows of tapered roller bearings fitted one into each end of a common bearing cup with their respective bearing cones having an inner diameter dimensioned to provide an interference fit with the shaft journal and with a cylindrical sleeve or spacer positioned between the cones providing accurate spacing on the journal. Seals mounted within each end of the bearing cup provide sealing contact with wear rings bearing against the outer ends of the respective bearing cones at each end of the assembly.
In a typical rail car installation, the axle journal is machined with a fillet at the inboard end, and a backing ring having a surface complementary to the contour of the fillet and an abutment surface for engaging the inboard end of the inner wear ring accurately positions the bearing assembly on the journal. An end cap mounted on the end of the axle by bolts threaded into bores in the end of the axle engages the outboard wear ring and clamps the entire assembly on the end of the axle. The wear rings typically have an inner diameter dimensioned to provide an interference fit with the journal over at least a portion of their length so that the entire assembly is pressed as a unit onto the end of the journal shaft. A bearing of this type is illustrated, for example, in U.S. Pat. No. 3,494,682.
In use of bearings of the type described above, high static and dynamic loading results in flexure of the heavy axle or shaft, which flexure results in relative movement between the journal surface and the wear rings fitted thereon. This movement is greatest at the inboard wear ring and frequently results in fretting between the wear ring and the journal surfaces, and fretting or end face wear between the end of the wear ring and the abutting end of the inboard bearing cone. This fretting can, over time, produce a groove in the journal surface and an enlargement of the ring bore, and wear between the end of the wear ring and the bearing cone, which together may result in the wear ring becoming so loose as not to remain perfectly concentric with the journal surface, and this may ultimately produce seal failure.
One proposal to solve the journal fretting and end face wear problem is illustrated in U.S. Pat. No. 5,017,025 which discloses use of a seal wear ring having an internal diameter greater than the diameter of the shaft to provide a space between the wear ring and shaft throughout the length of the wear ring. The backing ring is provided with a counterbore and shoulder dimensioned to receive the end of the wear ring, with an inference fit, to align the wear ring relative to the axis of rotation. It has been found, however, that it is not always possible to obtain precise axial alignment when the bearing is installed, and further that when pressing the bearing onto the shaft, the end of the wear ring is not always precisely aligned with the counterbore in the backing ring so that the heavy pressing loads can mar the backing ring and/or shoulder which, in turn, can result in further misalignment. Even though there is no contact between the shaft and wear ring, any misalignment can lead to excessive seal wear and ultimately seal failure, and to accelerated end face wear between the seal ring and bearing cone. Even under the exacting manufacturing standards conventionally employed in the bearing art, machining tolerances can result in some eccentricity which can be magnified along the length of the wear ring which, in turn, can result in concentrated loads and localized end face wear as well as excessive seal wear.